Resonant converter and switching power supply device

Abstract

A resonant inverter includes a first switch element and a second switch element that are alternately turned on and off, a first capacitor and a second capacitor, a first inverter section constituted by the first switch element and the first capacitor, and a second inverter section constituted by the second switch element and the second capacitor. A first coil and the first capacitor constitute a first resonant circuit included in the first inverter section, and the first coil and the second capacitor constitute a second resonant circuit included in the second inverter section, thereby forming a resonant converter.

What is claimed is: 
     
       1. A resonant converter comprising:
 a step-down converter including:
 a first switch element; 
 a second switch element; and 
 a first coil connected to the first and second switch elements; and 
 
 a resonant inverter including:
 a third switch element and a fourth switch element that are alternately turned on and off; 
 a first capacitor and a second capacitor connected in parallel to the third switch element and the fourth switch element, respectively; 
 a first inverter section constituted by the third switch element and the first capacitor, the first inverter section including a first resonant circuit constituted by the first coil and the first capacitor; 
 a second inverter section constituted by the fourth switch element and the second capacitor, the second inverter section including a second resonant circuit constituted by the first coil and the second capacitor; and 
 a fifth resonant circuit constituted by a series connection of a fifth coil and a fifth capacitor placed between one end of the third switch element and one end of the fourth switch element. 
 
 
     
     
       2. The resonant converter according to  claim 1 , wherein
 the first inverter section further includes a third resonant circuit, and 
 the second inverter section further includes a fourth resonant circuit. 
 
     
     
       3. The resonant converter according to  claim 2 , wherein
 the third resonant circuit of the first inverter section is constituted by a series connection of a second coil and a third capacitor placed between one end and the other end of the third switch element, and 
 the fourth resonant circuit of the second inverter section is constituted by a series connection of a fourth coil and a fourth capacitor placed between one end and the other end of the fourth switch element. 
 
     
     
       4. The resonant inverter according to  claim 2 , further comprising:
 a transformer connected to the first and second switch elements, 
 wherein the first coil is formed of a leakage inductance of the transformer. 
 
     
     
       5. The resonant converter according to  claim 2 , wherein
 the first and second switch elements are driven in accordance with a fixed duty cycle, and the third switch element and the fourth switch element are driven in accordance with a fixed duty cycle. 
 
     
     
       6. The resonant converter according to  claim 2 , wherein
 when a drive frequency for driving the third switch element or the fourth switch element is denoted by Fs, a drive frequency for driving the first and second switch elements is 2Fs. 
 
     
     
       7. A switching power supply device comprising:
 the resonant converter according to  claim 2 ; 
 a resonant rectifier connected to the resonant converter; 
 a voltage detection circuit that detects an output voltage of the resonant rectifier; 
 a hysteresis comparator that outputs a control signal for driving the first and second switch elements when a detected value of the output voltage reaches a first threshold, and outputs a control signal for stopping the first and second switch elements when the detected value reaches a second threshold; and 
 a drive circuit that controls the first and second switch elements in accordance with the control signal. 
 
     
     
       8. The resonant inverter according to  claim 1 , further comprising:
 a transformer connected to the first and second switch elements, 
 wherein the first coil is formed of a leakage inductance of the transformer. 
 
     
     
       9. The resonant converter according to  claim 8 , wherein
 the first and second switch elements are driven in accordance with a fixed duty cycle, and the third switch element and the fourth switch element are driven in accordance with a fixed duty cycle. 
 
     
     
       10. The resonant converter according to  claim 8 , wherein
 when a drive frequency for driving the third switch element or the fourth switch element is denoted by Fs, a drive frequency for driving the first and second switch elements is 2Fs. 
 
     
     
       11. A switching power supply device comprising:
 the resonant converter according to  claim 8 ; 
 a resonant rectifier connected to the resonant converter; 
 a voltage detection circuit that detects an output voltage of the resonant rectifier; 
 a hysteresis comparator that outputs a control signal for driving the first and second switch elements when a detected value of the output voltage reaches a first threshold, and outputs a control signal for stopping the first and second switch elements when the detected value reaches a second threshold; and 
 a drive circuit that controls the first and second switch elements in accordance with the control signal. 
 
     
     
       12. The resonant converter according to  claim 1 , wherein
 the first and second switch elements are driven in accordance with a fixed duty cycle, and the third switch element and the fourth switch element are driven in accordance with a fixed duty cycle. 
 
     
     
       13. The resonant converter according to  claim 12 , wherein
 when a drive frequency for driving the third switch element or the fourth switch element is denoted by Fs, a drive frequency for driving the first and second switch elements is 2Fs. 
 
     
     
       14. A switching power supply device comprising:
 the resonant converter according to  claim 12 ; 
 a resonant rectifier connected to the resonant converter; 
 a voltage detection circuit that detects an output voltage of the resonant rectifier; 
 a hysteresis comparator that outputs a control signal for driving the first and second switch elements when a detected value of the output voltage reaches a first threshold, and outputs a control signal for stopping the first and second switch elements when the detected value reaches a second threshold; and 
 a drive circuit that controls the first and second switch elements in accordance with the control signal. 
 
     
     
       15. A switching power supply device comprising:
 the resonant converter according to  claim 1 ; 
 a resonant rectifier connected to the resonant converter; 
 a voltage detection circuit that detects an output voltage of the resonant rectifier; 
 a hysteresis comparator that outputs a control signal for driving the first and second switch elements when a detected value of the output voltage reaches a first threshold, and outputs a control signal for stopping the first and second switch elements when the detected value reaches a second threshold; and 
 a drive circuit that controls the first and second switch elements in accordance with the control signal. 
 
     
     
       16. The resonant converter according to  claim 1 , wherein
 when a drive frequency for driving the third switch element or the fourth switch element is denoted by Fs, a drive frequency for driving the first and second switch elements is 2Fs. 
 
     
     
       17. A resonant converter comprising:
 a step-down converter including:
 a first switch element; 
 a second switch element; and 
 a first coil connected to the first and second switch elements; and 
 
 a resonant inverter including:
 a third switch element and a fourth switch element that are alternately turned on and off; 
 a first capacitor and a second capacitor connected in parallel to the third switch element and the fourth switch element, respectively; 
 a first inverter section constituted by the third switch element and the first capacitor, the first inverter section including a first resonant circuit constituted by the first coil and the first capacitor; and 
 a second inverter section constituted by the fourth switch element and the second capacitor, the second inverter section including a second resonant circuit constituted by the first coil and the second capacitor, 
 
 wherein when a drive frequency for driving the third switch element or the fourth switch element is denoted by Fs, a drive frequency for driving the first and second switch elements is 2Fs. 
 
     
     
       18. A switching power supply device comprising:
 the resonant converter according to  claim 17 ; 
 a resonant rectifier connected to the resonant converter; 
 a voltage detection circuit that detects an output voltage of the resonant rectifier; 
 a hysteresis comparator that outputs a control signal for driving the first and second switch elements when a detected value of the output voltage reaches a first threshold, and outputs a control signal for stopping the first and second switch elements when the detected value reaches a second threshold; and 
 a drive circuit that controls the first and second switch elements in accordance with the control signal.